1. Field Of The Invention
The invention relates to new Ames-test-negative chain-lengthening agents or cross-linking agents for polyurethane.
2. Prior Art
Production of polyurethanes according to the isocyanate polyaddition process is known. For example, compounds having reactive hydrogen atoms, such as polyesters with terminal OH groups, are reacted with diisocyanates to form a prepolymer (West German PS No. 1,240,654), which is then brought to reaction in a second step with a chain-lengthening agent or a cross-linking agent, usually an aromatic diamine. The resultant pourable reaction mass can then be cured in a mold over a prolonged period. It is essential that the prepolymers do not react too fast with the chain-lengthening agents or cross-linking agents so that an adequate processing time in the liquid phase is assured. Especially primary and secondary di- and poly-amines, preferably aromatic diamines, are the choice for this purpose.
It has been found that the best processing characteristics can be attained if a substitutent is in the ortho position on the amino group. With these compounds, most of all 4,4'-methylene-bis(2-chloroaniline), (MOCA), it is possible to obtain elastomers with particularly good properties with a good processing time [Wright et al., Solid Polyurethane Elastomers, p. 125, MacLaren, London, (1969)]. But a significant disadvantage of MOCA, which resulted in its being banned in some countries, is its carcinogenicity and mutagenicity, detected by the positive Ames test [Ames et al., Proc. Nat. Acad. Sci. USA, vol. 70, No. 3, pp. 782-786 and No. 8, pp. 2281-2285].
Further, in practice chain-lengthening agents have been used which have alkyl groups in the ortho position, including preferably diaminodiphenylmethanes alkyl-substituted in the ortho position, such as, 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane or 3,5-dimethyl-3',5'-diisopropyl-4,4'-diaminodiphenylmethane (West German OS No. 3,126,436). But with these amines the pot lives become so short that no reasonable processing time is any longer possible.
The opinion is widespread that the best results can be obtained only with amines as chain-lengthening agents or cross-linking agents which exhibit electron-attracting radicals, e.g., halogen radicals, in the ortho position [Hepburn, Polyurethane Elastomers, Appl. Science Publ. (1982) p. 57; Becher, Braun, Kunstoff Handbuch [Plastics Manual], Vol. 7, Polyurethanes, 2nd Rev. Ed. (1983), p. 100].
There was even a willingness to put up with poor toxicological data as well as considerable disadvantages in the temperature stability of individual o-halogenated compounds. Thus, in the case of MOCA, for example, the maximum working temperature is not to exceed 140.degree. C. to avoid undesirable bubble formation by generation of gas in the product as a result of decomposition reactions.